Slurry for CMP, polishing method and method of manufacturing semiconductor device

ABSTRACT

Disclosed is a CMP slurry comprising a first colloidal particle having a primary particle diameter ranging from 5 nm to 30 nm and an average particle diameter of d1, the first colloidal particle being incorporated in an amount of w1 by weight and a second colloidal particle having a primary particle diameter larger than that of the first colloidal particle and an average particle diameter of d2, the second colloidal particle being formed of the same material as that of the first colloidal particle and incorporated in an amount of w2 by weight, wherein d1, d2, w1 and w2 are selected to concurrently meet following conditions (A) and (B) excluding situations where d1, d2, w1 and w2 concurrently meet following conditions (C) and (D):
 
3≦ d 2/ d 1≦8  (A)
 
0.7≦ w 1/( w 1+ w 2)≦0.97  (B)
 
3≦ d 2/ d 1≦5  (C)
 
0.7≦ w 1/( w 1 +w 2)≦0.9.  (D)

CROSS-REFERENCE TO RELATED-APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2003-173263, filed Jun. 18, 2003,the entire contents of which are incorporated herein by reference.

This is a division of application Ser. No. 10/838,261, filed May 5,2004, now U.S. Pat. No. 7,060,621 the disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a slurry to be used for CMP (ChemicalMechanical Polishing), a polishing method using the slurry, and a methodof manufacturing a semiconductor device.

2. Description of the Related Art

It is expected that the integration of semiconductor elements inhigh-performance LSIs of the next generation will be inevitably furtherenhanced. For example, the design rule of damascene wirings to be formedby CMP is expected to become so severe that the line width of wirings iswill be confined within the range of 0.07 to 30 μm and the filmthickness of wirings will be confined to not more than 100 nm.

Therefore, in designing a slurry for CMP, it is required to take theseconditions into account and to employ abrasive grains which aresufficiently small relative to the line width of wirings so as to makeit possible to perform fine and delicate polishing. For example, therehas been proposed employing a slurry comprising two or more colloidalsilica whose primary particle diameter is controlled. These slurries arecapable of polishing a polishing surface while suppressing thegeneration of erosion and scratching if the polishing surface isconstituted of a soft material or by a sole material, thereby enablingthese slurries to exhibit excellent CMP performances. However, if thepolishing surface is constituted of a hard material such as Ta or SiO₂,these slurries are incapable of performing the polishing at asufficiently high polishing speed. Further, there is a problem that ifthe polishing surface is constituted of two or more materials, it isdifficult to adjust the polishing balance so as to enable pluralmaterials to be polished at the same polishing rate as each other.

BRIEF SUMMARY OF THE INVENTION

A CMP slurry according to one aspect of the present invention comprisesa CMP slurry comprising a first colloidal particle having a primaryparticle diameter ranging from 5 nm to 30 nm and an average particlediameter of d1, the first colloidal particle being incorporated in anamount of w1 by weight; and a second colloidal particle having a primaryparticle diameter larger than that of the first colloidal particle andan average particle diameter of d2, the second colloidal particle beingformed of the same material as that of the first colloidal particle andincorporated in an amount of w2 by weight; wherein d1, d2, w1 and w2 areselected to concurrently meet following conditions (A) and (B) excludingsituations where d1, d2, w1 and w2 concurrently meet followingconditions (C) and (D):3≦d2/d1≦8   (A)0.7≦w1/(w1+w2)≦0.97   (B)3≦d2/d1≦5   (C)0.7≦w1/(w1+w2)≦0.9   (D)

A polishing method according to one aspect of the present inventioncomprises a polishing method comprising: contacting a polishing surfaceof a semiconductor substrate with a polishing pad attached to aturntable; and dropping a CMP slurry onto the polishing pad to polishthe polishing surface, the CMP slurry comprising a first colloidalparticle having a primary particle diameter ranging from 5 nm to 30 nmand an average particle diameter of d1, the first colloidal particlebeing incorporated in an amount of w1 by weight and a second colloidalparticle having a primary particle diameter larger than that of thefirst colloidal particle and an average particle diameter of d2, thesecond colloidal particle being formed of the same material as that ofthe first colloidal particle and incorporated in an amount of w2 byweight, d1, d2, w1 and w2 being selected to concurrently meet followingconditions (A) and (B) excluding situations where d1, d2, w1 and w2concurrently meet following conditions (C) and (D):3≦d2/d1≦8   (A)0.7≦w1/(w1+w2)≦0.97   (B)3≦d2/d1≦5   (C)0.7≦w1/(w1+w2)≦0.9   (D)

A method of manufacturing a semiconductor device according to one aspectof the present invention comprises a method of manufacturing asemiconductor device comprising forming an insulating film above asemiconductor substrate; forming a recessed portion in the insulatingfilm; depositing a wiring material inside the recessed portion and onthe insulating film through a barrier film to form a conductive layer;and removing the conductive layer deposited on the insulating film byCMP using a CMP slurry to expose the surface of the insulating filmwhile selectively leaving the conductive layer in the recessed portion,the CMP slurry comprising a first colloidal particle having a primaryparticle diameter ranging from 5 nm to 30 nm and an average particlediameter of d1, the first colloidal particle being incorporated in anamount of w1 by weight and a second colloidal particle having a primaryparticle diameter larger than that of the first colloidal particle andan average particle diameter of d2, the second colloidal particle beingformed of the same material as that of the first colloidal particle andincorporated in an amount of w2 by weight, d1, d2, w1 and w2 beingselected to concurrently meet following conditions (A) and (B) excludingsituations where d1, d2, w1 and w2 concurrently meet followingconditions (C) and (D):3≦d2/d1≦8   (A)0.7≦w1/(w1+w2)≦0.97   (B)3≦d2/d1≦5   (C)0.7≦w1/(w1+w2)≦0.9   (D)

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a graph showing the particle size distribution of colloidalparticle;

FIGS. 2A and 2B are cross-sectional views each illustrating, stepwise,the method of manufacturing a semiconductor device according to oneembodiment of the present invention;

FIG. 3 is a perspective view schematically illustrating a state of CMP;

FIG. 4 is a cross-sectional view illustrating one step in themanufacturing method of a semiconductor device where conventional slurryfor CMP is employed; and

FIGS. 5A and 5B are cross-sectional views each illustrating, stepwise,the method of manufacturing a semiconductor device according to anotherembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Next, the specific embodiments of the present invention will beexplained as follows.

In the slurry for CMP (hereinafter referred to also as CMP slurry)according to the embodiments of the present invention, examples ofcolloidal particle include colloidal silica particle. This colloidalsilica particle can be obtained by the hydrolysis, by sol-gel method, ofsilicon alkoxide compounds such as Si(OC₂H₅)₄, Si(sec-OC₄H₉)₄, Si(OCH₃)₄and Si(OC₄H₉)₄. As for the colloidal particles, it is possible to employcolloidal alumina.

Among these colloidal particles, those where the primary particlediameter thereof ranges from 5 nm to 30 nm can be employed as a firstcolloidal particle. If the primary particle diameter of the colloidalparticle is less than 5 nm, the polishing property of the slurrycontaining such a colloidal particle as an abrasive grain would bedegraded. On the other hand, if the primary particle diameter of thecolloidal particle is larger than 30 nm, erosion and scratching would becaused on a polishing surface on the occasion of polishing the polishingsurface by using slurry containing such a colloidal particle as anabrasive grain. The primary particle diameter of the first colloidalparticle should preferably be confined within the range of 10 nm to 20nm.

The particle whose primary particle diameter is larger than that of thefirst colloidal particle and which is formed of the same material asthat of the first colloidal particle is employed as the second colloidalparticle. However, the average particle diameter and mixing ratio of thesecond colloidal particle are selected so as to meet a specificrelationship.

In the embodiments of the present invention, the first and the secondcolloidal particles differ in the primary particle diameter from eachother have respectively a very sharp size distribution which does notoverlap with a very sharp size distribution of the other colloidalparticles. The graph of FIG. 1 shows one example of the sizedistribution wherein an average particle diameter (d1) of the firstcolloidal silica is 15 nm, an average particle diameter (d2) of thesecond colloidal silica is 75 nm, and the ratio in difference ofparticle diameters (d2/d1) is 5.

The primary particle diameter of the colloidal silica can be determinedthrough observation by an SEM or TEM. For example, after being diluted,slurry is uniformly deposited on a sample table and heated to evaporatethe liquid component to form a layer. Thereafter, gold for example isvapor-deposited on the layer and the resultant layer is observed by anSEM and photographed at a magnification of 100,000 to 500,000 times.Thereafter, the maximum particle diameter of the particle is measured byusing calipers. Then, a diameter is determined by drawing aperpendicular bisector relative to the maximum particle diameter, and anadded average of values obtained from the diameter thus determined isassumed as the primary particle diameter. After 100 values in number ofthe primary particle diameter have been determined, these values areemployed to draw a cumulative grain size curve, from which a primaryparticle diameter at 50% is assumed as an average particle diameter.

The CMP slurry according to the embodiments of the present invention canbe prepared by dispersing the abrasive grain containing the firstcolloidal particle and the second colloidal particle in water such aspure water. The abrasive grain containing the first colloidal particleand the second colloidal particle should preferably be included in theslurry at a ratio of 0.1 wt % to 20 wt %. If the content of the abrasivegrain is less than 0.1 wt %, the polishing properties of the slurrycontaining such an abrasive grain would be degraded. On the other hand,if the content of the abrasive grain exceeds 20 wt %, erosion andscratch would be caused on the polishing surface on the occasion ofpolishing the polishing surface by using a slurry containing such thisabrasive grain. The content of the abrasive grain should more preferablybe confined within the range of 0.5 wt % to 10 wt %.

If required, the CMP slurry according to the embodiments of the presentinvention may be formulated so as to include an oxidizing agent, anoxidation inhibitor, a surfactant, etc.

As for the oxidizing agent, it is possible to employ ammoniumpersulfate, potassium persulfate, hydrogen peroxide, ferric nitrate,ammonium cerium nitrate, etc. These oxidizing agents should preferablybe included in the slurry at a ratio of 0.1 to 5% by weight.

As for the oxidation inhibitor, they include organic acids such asquinaldinic acid, quinolinic acid, malonic acid, oxalic acid, succinicacid, etc.; amino acids such as glycine, alanine, tryptophan, etc.; BTA(benzotriazole), etc. Among them, in terms of handling, quinaldinicacid, quinolinic acid and glycine are more preferable for use. Theoxidation inhibitor should preferably be included in the slurry at aratio of 0.01 to 3% by weight.

As for the surfactant, they include, for example, anionic surfactants,cationic surfactants and nonionic surfactants. These surfactants arecapable of minimizing erosion and scratching on the occasion ofpolishing. As for specific examples of the surfactants, they includedodecylbenzene sulfonic acid, polyoxyethylene alkylamine,polyoxyethylene lauryl ether, acetylene diol-based nonion, etc. Thesurfactants should preferably be included in the slurry at a ratio of0.01 to 1% by weight.

As for the pH of the CMP slurry according to the embodiments of thepresent invention, there is not any particular limitation, and hence,the CMP slurry may be employed with the pH thereof being falling withinthe range of 0.5 to 12. The pH of the CMP slurry can be adjusted to 11or so by using, for example, KOH as a pH adjustor.

Since the ratio in difference of particle diameters as well as themixing ratio of two colloidal particles are regulated respectively to aspecific range in the CMP slurry according to the embodiments of thepresent invention, it is possible, through the employment of this CMPslurry, to polish a polishing surface while suppressing erosion orscratching on the polishing surface. Moreover, it is now also possible,through the employment of this CMP slurry, to polish a surface of hardmaterials at substantially the same high polishing rate as that inpolishing a soft material.

Embodiment 1

First of all, a first colloidal silica having an average particlediameter (d1) of 15 nm, and a second colloidal silica having an averageparticle diameter (d2) which was larger than that of the first colloidalsilica were variously combined to prepare various slurries.

Specifically, the average particle diameter (d2) of the second colloidalsilica was variously altered within the range of 15 nm to 135 nm toobtain various ratios in difference of particle diameters (d2/d1)ranging from 1 to 9. Further, the weight (w1) of the first colloidalsilica relative to the total weight (w1+w2) of colloidal silica wasaltered within the range of 0.65 to 1.0 to prepare various colloidalsilica mixtures.

2 wt % of colloidal silica mixture, 2 wt % of ammonium persulfate as anoxidizing agent, 0.2 wt % of quinaldinic acid, 0.3 wt % of quinolinicacid, 0.3 wt % of glycine as an oxidation inhibitor, and an additivewere added to pure water to obtain various solutions, to which KOH wasadded thereto to adjust the pH thereof to 9 to prepare various slurries.

By using these slurries thus obtained, a Cu damascene wiring was formed.FIGS. 2A and 2B are cross-sectional views each illustrating the steps offorming the Cu damascene wiring.

First of all, as shown in FIG. 2A, an insulating film 11 was depositedon a semiconductor substrate 10 having semiconductor elements formedthereon, and holes “A” 0.1 μm in width and 0.1 μm in depth were formed.Further, by a sputtering method and a plating method, a Cu film 13having a thickness of 150 nm for forming wirings was deposited, via abarrier film, i.e. a Ta film 12 having a thickness of 10 nm, the entiresurface of the insulating film (SiO₂ film) 11 provided with the holes“A”.

Then, the redundant portions of the Ta film 12 and the Cu film 13 wereremoved by CMP to expose the surface of the insulating film 11 as shownin FIG. 2B, thus selectively leaving the Ta film 12 and the Cu film 13in the holes “A”.

This polishing by CMP was performed as follows by using IC1000(trademark; Rodel Nitta Co., Ltd.) as a polishing pad and the slurriesprepared as described above. Namely, as shown in FIG. 3, while rotatinga turntable 20 having a polishing pad 21 attached thereto at a speed of100 rpm, a top ring 23 holding a semiconductor substrate 22 was allowedto contact with the turntable 20 at a polishing load of 300 gf/cm². Therotational speed of the top ring 23 was set to 102 rpm, and the slurry27 was fed onto the polishing pad 21 from a slurry supply nozzle 25 at aflow rate of 200 cc/min. Incidentally, FIG. 3 also shows a water supplynozzle 24 and a dresser 26.

By using each slurry, the Ta film 12, the Cu film 13 and the SiO₂ film11 were polished to investigate the polishing rate, dishing andscratching of each of these films to evaluate these slurries. Namely,these slurries were respectively evaluated in such a manner that wheneach slurry satisfied all of the conditions that the polishing rate ofany of the Cu film 13, the Ta film 12 and the SiO₂ film 11 was not lessthan 30 nm/min., the erosion was less than 20 nm, and the number ofscratches on the surfaces of the Cu film 13 and the SiO₂ film 11 wasless than 10/cm², the slurry was considered very good and marked by asymbol of “⊚”.

When the number of scratches on the surfaces of the Cu film 13 and theSiO₂ film 11 was not less than 10/cm² but less than 20/cm², the slurrywas considered good and marked by a symbol of “O”. When the number ofscratches on the surfaces of the Cu film 13 and the SiO₂ film 11 was notless than 20/cm² but less than 40/cm², the slurry was considered fairand marked by a symbol of “Δ”. Further, when the polishing rate of anyone of the Ta film 12 and the SiO₂ film 11 was less than 30 nm/min., theslurry was considered fair and marked by a symbol of “Δ”. When thepolishing rate of both of the Ta film 12 and the SiO₂ film 11 was lessthan 30 nm/min., the slurry was considered bad and marked by a symbol of“x”. When the number of scratches on the surfaces of the Cu film 13 andthe SiO₂ film 11 was not less than 40/cm², the slurry was considered badand marked by a symbol of “x”.

The results thus obtained are summarized in the following Table 1.

TABLE 1 Ratio in difference of particle diameter (d2/d1) 1 2 3 4 5 6 7 89 w1/(w1 + w2) 0.65 X X X X X X X X X 0.7 X X X X Δ ◯ ◯ ◯ X 0.75 X X X XΔ ◯ ◯ ◯ X 0.8 X X X X Δ ⊚ ⊚ ◯ X 0.85 X X X X Δ ⊚ ⊚ ◯ X 0.9 X X Δ Δ Δ ⊚ ⊚◯ X 0.91 X X ◯ ◯ ⊚ ⊚ ⊚ ◯ X 0.92 X X ⊚ ⊚ ⊚ ⊚ ⊚ ◯ X 0.93 X X ⊚ ⊚ ⊚ ⊚ ⊚ ◯ X0.94 X X ⊚ ⊚ ⊚ ⊚ ⊚ ◯ X 0.95 X X ⊚ ⊚ ⊚ ⊚ ⊚ ◯ X 0.96 X X ⊚ ⊚ ⊚ ⊚ ⊚ ◯ X0.97 X X ◯ ◯ ◯ ◯ ◯ ◯ X 0.98 X X X X X X X X X 1 X X X X X X X X X

In the region of “⊚”, since all of the Cu film 13, the Ta film 12 andthe SiO₂ film 11 can be polished at a polishing rate of not less than 30nm/min., the slurries falling within this region are especially suitedfor forming a Cu multilayer wiring. Since it is possible, through theemployment of the slurries falling within this region, to obviate thegeneration of short-circuit of wirings resulting from a residue of Cuand moreover to secure a sufficient power to polish the SiO₂ film, it isnow possible to perform the polishing so as to minimize the developmentof step portion of the underlying layer (STI or W plug) on the occasionof the CMP of Cu layer constituting an uppermost layer.

Even in the region of “O”, since most of the scratches generated arerelatively shallow, hey were not fatal to a semiconductor device. Theslurries which fall within the regions of “⊚” and “O” meet theconditions for the first colloidal particle and the second colloidalparticle according to the embodiments of the present invention.

If the polishing rate of any one of the Ta film 12 and the SiO₂ film 11is less than 30 nm/min., it would be impossible to polish a softmaterial such as a Cu film and the aforementioned hard materials atsubstantially an equivalent polishing rate to each other.

Therefore, when the Ta film 12 and the Cu film 13 are selectively buriedin the holes “A” as shown in FIG. 2B, it is required at first to removea redundant portion of the Cu film 13 which is disposed over the Ta film12 and then to separately perform the CMP (touch-up step) of the Ta film12 to expose the surface of the insulating film 11 as shown in FIG. 4.

In the region of “Δ”, even though the total number of scratchesgenerated was relatively small, scratches each having such a large depththat is fatal to a semiconductor device existed at a ratio of 10/cm² ormore.

It is now possible, through the employment of the CMP slurry accordingto the embodiments of the present invention, to remove redundantportions of the Cu film and Ta film by a single polishing step and toform a damascene wiring. Therefore, the CMP slurry according to theembodiment of the present invention is advantageous in terms of reducingnot only the number of manufacturing steps but also the manufacturingcost.

It was possible to obtain almost the same effects as described aboveeven if the material of the barrier film was changed to Ti, Nb, V, W orMo. Namely, irrespective of the materials of the barrier film, it is nowpossible, through the employment of the CMP slurry according to theembodiment of the present invention, to polish the barrier film togetherwith a wiring material.

Embodiment 2

The CMP slurry according to the embodiments of the present inventionwere capable of application to the formation of STI (Shallow trenchisolation). FIGS. 5A and 5B are cross-sectional views each illustratingthe process of forming the STI.

First of all, as shown in FIG. 5A, a trench was formed on asemiconductor substrate 30 having a CMP stopper film 31, and then, aninsulating film 32 was deposited thereon. In this case, SiN was employedas the CMP stopper film 31. As for the insulating film 32, acoating-type insulating film such as an organic SOG can be employed.

Then, a redundant portion of the insulating film 32 was removed by CMPusing the slurry according to one embodiment of the present invention toexpose the surface of the CMP stopper film 31 as shown in FIG. 5B.

In this embodiment, the slurry was prepared by using a first colloidalsilica (an average particle diameter d1: 10 nm), and a second colloidalsilica (an average particle diameter d2: 60 nm). The ratio in differenceof particle diameters (d2/d1) was 6, and these two kinds of colloidalsilica were mixed together so as to adjust the weight ratio of the firstcolloidal silica (w1/(w1+w2)) to 0.9 to prepare an abrasive grain. Thisabrasive grain was dispersed in pure water to obtain a solutioncontaining this abrasive grain at a concentration of 10 wt % and the pHof the solution was adjusted to 11 by using KOH as a pH adjustor.

Then, by using the slurry thus obtained, an insulating film 32 waspolished under the following conditions.

Flow rate of slurry: 300 cc/min;

Polishing pad: IC1000 (trademark; Rodel Nitta Co., Ltd.);

Load: 300 gf/cm².

Rotational speed of the top ring and turntable were both set to 100 rpm,and the polishing was performed for 3 minutes. Since the concentrationof the particles in the slurry employed herein was relatively high, theresultant environment was such that scratches were liable to begenerated.

Due to the employment of the slurry according to this embodiment, thenumber of the scratches generated on the surface of wafer after thepolishing was confined to only two, and the erosion was suppressed to 30nm or less. Thus, it was confirmed that the slurry according to thisembodiment was effective in achieving the same effects as describedabove even in the CMP of the insulating film deposited on the CMPstopper film which was vulnerable to scratches.

The fact that the step portion “B” shown in FIG. 5B can be effectivelyflattened is also one of the characteristics of the CMP slurry of thisembodiment of the present invention. In this embodiment, the scraping inthe CMP was performed down to the CMP stopper film 31. However, the CMPusing the CMP slurry may be performed in such a process that only thestep portion “B” is flattened and the CMP is stopped at a midway of theinsulating film 32.

For the purpose of comparison, a slurry was prepared in such a manner asto adjust the weight ratio of the first colloidal silica (w1/(w1+w2)) to0.9 by following the same procedures as described above except that thesecond colloidal silica was selected so as to regulate the ratio indifference in particle diameters (d2/d1) to 3.

By using this slurry thus obtained, the polishing of the insulating filmwas performed under the same conditions as described above. As a result,the number of scratches generated on the surface of the wafer after thepolishing was 320 and the erosion was found to be 35 nm approximately.

As described above, it has been confirmed that if the conditions on thefirst and second colloidal particles exceed beyond the ranges defined bythe embodiments of the present invention, the state of polished surfaceafter the polishing step would be degraded.

As explained above, according to the embodiments of the presentinvention, it is possible to provide a CMP slurry which is capable ofsuppressing the generation of erosion as well as scratching and alsocapable of polishing a polishing surface constituted of two or morematerials differing in hardness from each other at a practicallyacceptable polishing rate and at an equivalent polishing rate to eachother. According to another embodiment of the present invention, it ispossible to provide a polishing method which is capable of suppressingthe generation of erosion as well as scratching and also capable ofpolishing the polishing surface at a practically acceptable polishingrate. According to a further embodiment of the present invention, it ispossible to provide a method of manufacturing a semiconductor devicewhich is excellent in reliability.

According to the embodiments the present invention, it is now possibleto manufacture a semiconductor device of high-performance andhigh-processing speed and having fine wirings of 0.1 μm of less indesign rule which will be demanded in the wirings of the nextgeneration. Therefore, the present invention will be very valuable froman industrial viewpoint.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A CMP slurry comprising: a first colloidal particle having a primaryparticle diameter ranging from 5 nm to 30 nm and an average particlediameter of d1, the first colloidal particle being incorporated in anamount of w1 by weight; and a second colloidal particle having a primaryparticle diameter larger than that of the first colloidal particle andan average particle diameter of d2, the second colloidal particle beingformed of the same material as that of the first colloidal particle andincorporated in an amount of w2 by weight; wherein d1, d2, w1 and w2 areselected to concurrently meet following conditions (A) and (B) excludingsituations where d1, d2, w1 and w2 concurrently meet followingconditions (C) and (D):3≦d2/d1≦8   (A)0.7≦w1/(w1+w2)≦0.97   (B)3≦d2/d1≦5   (C)0.7≦w1/(w1+w2)≦0.9   (D).
 2. The CMP slurry according to claim 1,wherein the first colloidal particle and the second colloidal particleare both formed of colloidal silica particle.
 3. The CMP slurryaccording to claim 1, wherein a total content of the first and secondcolloidal particles is within the range of 0.1 wt % to 20 wt % of theslurry.
 4. The CMP slurry according to claim 1, wherein the diameter ofprimary particle of the first colloidal particle is within the range of10 nm to 20 nm.
 5. The CMP slurry according to claim 1, wherein a totalcontent of the first and second colloidal particles is within the rangeof 0.5 wt % to 10 wt % of the slurry.
 6. A CMP slurry comprising: afirst colloidal particle having a primary particle diameter ranging from5 nm to 30 nm and an average particle diameter of d1, the firstcolloidal particle being incorporated in an amount of w1 by weight; anda second colloidal particle having a primary particle diameter largerthan that of the first colloidal particle and an average particlediameter of d2, the second colloidal particle being formed of the samematerial as that of the first colloidal particle and incorporated in anamount of w2 by weight; wherein d1, d2, w1 and w2 are selected toconcurrently meet following conditions (1) and (2):3≦d2/d1≦8   (1)0.9<w1/(w1+w2)≦0.97   (2).
 7. The CMP slurry according to claim 1,wherein the first colloidal particle and the second colloidal particleare both formed of colloidal silica particle.
 8. The CMP slurryaccording to claim 1, wherein a total content of the first and secondcolloidal particles is within the range of 0.1 wt % to 20 wt % of theslurry.
 9. The CMP slurry according to claim 1, wherein the diameter ofprimary particle of the first colloidal particle is within the range of10 nm to 20 nm.
 10. The CMP slurry according to claim 1, wherein a totalcontent of the first and second colloidal particles is within the rangeof 0.5 wt % to 10 wt % of the slurry.
 11. A CMP slurry comprising: afirst colloidal particle having a primary particle diameter ranging from5 nm to 30 nm and an average particle diameter of d1, the firstcolloidal particle being incorporated in an amount of w1 by weight; anda second colloidal particle having a primary particle diameter largerthan that of the first colloidal particle and an average particlediameter of d2, the second colloidal particle being formed of the samematerial as that of the first colloidal particle and incorporated in anamount of w2 by weight; wherein d1, d2, w1 and w2 are selected toconcurrently meet following conditions (1) and (2):5<d2/d1≦8   (1)0.7≦w1/(w1+w2)≦0.97   (2).
 12. The CMP slurry according to claim 11,wherein the first colloidal particle and the second colloidal particleare both formed of colloidal silica particle.
 13. The CMP slurryaccording to claim 11, wherein a total content of the first and secondcolloidal particles is within the range of 0.1 wt % to 20 wt % of theslurry.
 14. The CMP slurry according to claim 11, wherein the diameterof primary particle of the first colloidal particle is within the rangeof 10 nm to 20 nm.
 15. The CMP slurry according to claim 11, wherein atotal content of the first and second colloidal particles is within therange of 0.5 wt % to 10 wt % of the slurry.